Windblown materials found on the floors and sides of water-filled swimming pools consist generally of three classes of materials. A first class comprises a low-density related material of things such as water-soaked leaves, branches, and grass. A second class comprises a high-density related material of larger soil particles and small gravel or sand of greater than about 0.5 mm in diameter. A third class comprises the fine silt and dust of less than about 0.5 mm in diameter. Regular removal of these classes of materials, cumulatively called bottom material, is essential for aesthetic and health reasons.
Removal of low-density related material is generally accomplished in one of two ways. The first method adds water to the swimming pool and does not remove fine soil and silt or high-density related material. In this first method, a garden hose is attached to a vacuum head so that vacuum is created at the inlet of the device. The water from the garden hose is mixed with the water and materials drawn into the vacuum head from the bottom of the pool as they are all passed through a conduit to a bag with open, loose weaving. The looseness of weave of the bag is designed so that water, fine soil and silt, and high density related materials are able to pass through weave of the bag material leaving the lower density related materials behind.
The second method makes use of the pool's filter and pump apparatus to vacuum all three classes of materials from the pool bottom. This method begins with the vacuuming of water and bottom materials into a vacuum head and then passing that water/bottom materials mixture into a hose approximately 1-2. inches in diameter. The negative pressure required for this vacuuming is supplied by an existing pump normally drawing pool water through the pool filter. The inlet to the filter is changed from its normal operation so that inlet is attached to the other end of the hose attached to the vacuum head. Although fine soil and silt are effectively removed from the pool water in the pool filter, low-density related materials quickly overwhelm the pool filter and plug it. To extend the vacuuming process without plugging the pool filter, a prefilter is typically located between the vacuum head and the inlet to the pool filter.
This prefilter must be enclosed to maintain vacuum pressure from the pool filter pump. The prior art prefilters attach at one end to the hose carrying the flow of the water/bottom materials mixture from the vacuum head. That attachment is sealingly adapted to the top a cylindrical can perforated on its bottom and sides. The outlet of the prior art prefilters is sealingly adapted to the top rim of the perforated can to effect a flow of water through the inside of the can to the outside. The outlet of the prior art prefilter is adapted to attach to a length of hose or conduit leading to the inlet of the pool filter.
The low-density related materials tend to quickly plug the perforations of the can in the prior art prefilter because water-soaking makes them flexible and capable of being drawn onto the perforation openings by the vacuum water flow. Such a limitation reduces the effective vacuuming time when low-density related materials are a significant part of the bottom materials. In addition, the trapping of high-density related materials in the prefilter tends to accelerate the plugging of the prefilter by adding weight to the accumulation of low-density related material therein. The vacuum pump must be shut off and the prefilter cleaned before effective vacuuming is resumed. The can perforations of the prefilter are designed to permit passage of both fine soil and silt and high-density related material through the prefilter to the pool filter.
Although a combination of the first and second methods is effective for complete removal of all bottom material without plugging a prefilter, such a method is inefficient because the first method disturbs a part or all of the fine soil and silt from the pool bottom into the pool water. Typical settling time is about 30 to 45 minutes before the second method can be used to remove the other bottom material.